A doctor examines a patient at Community Health of South Florida on February 21, 2013 in Miami, Florida. US federal health spending will keep growing over the next 25 years but at a slower-than-expected pace, the Congressional Budget Office said Tuesday i

Avita Samuels has worked at the Mall of America in Minneapolis for the last four years, juggling a sales job with her studies in political science and law at the University of Minnesota. The 24-year-old has been the top sales associate for the last three years and works between 29 and 35 hours a week. But over the past few months, she said, she has watched as friends working in stores around her have their hours and benefits slashed – and she's worried that she will be next.

Forever 21, the clothing store, told staff last month in a memo leaked to the press that it planned to cut hours and reclassify some full-time workers as part- time. The move, which the company denied had anything to do with President Barack Obama's health reforms, the Affordable Care Act (ACA), will nevertheless help it avoid a mandate under the legislation requiring companies with 50 or more employees to offer those working 30 hours a week or more health insurance. Earlier this month, Seaworld, which operates 11 entertainment parks across the US, capped hours for part time workers at 28, down from 32, according to the Orlando Sentinel.

Other retailers, such as Trader Joe's and Home Depot have said they will no longer provide medical coverage for part-time employees, and will shift them instead to the public healthcare exchanges which open Tuesday, 1 October. Some employers have said their health costs will rise as a result of various provisions of the ACA, which takes full effect in 2015, when larger companies have to provide health benefits to full time workers or pay a $2,000 per-person fine.

The trend has caused fears among low-paid workers living on the breadline that they will be hit twice – by having their hours and thus earnings cut and by having to pay more for healthcare. Based on what she said is happening in the stores around her, Samuels is concerned she too will have her hours cut and with it her eligibility for company healthcare under the ACA.

"It's a really scary situation," said Samuels, who earns $9.25 an hour and is trying to reduce a student loan debt of close to $50,000. She currently receives subsidised healthcare through her university, but it runs out next year, when she had hoped her employer healthcare would kick in.

"Technically, I should be eligible," she said. "But at least 20 stores around me have cut hours. I live paycheck to paycheck. I have credit card debts. It's a balancing act. I'm afraid I won't be able to afford healthcare."

As one of the nation's lowest-paid workers, with little job security, Samuels is not alone in her fears that she may be worse off when the ACA takes full effect.

Following a callout to hourly workers who had experienced recent changes in hours or health benefits, the Guardian was contacted by employees and their families. Two of them said they were so concerned about additional costs of healthcare, they were considering not buying insurance at all.

Typing Samuel's average earnings of $15,000 a year and her state into the subsidy calculator on the Kaiser Family Foundation website, reveals that, if her employer did not offer healthcare and she were to enter a healthcare exchange, she would be eligible for government subsidy and would pay $300 a year towards the $1,449 cost of a plan. Samuels, who is already struggling financially, said this will represent a massive additional burden should her hours be cut by her employer.

Kavita Patel, a fellow in economic studies at the Brooking Institution who worked on healthcare reform in the White House, said: "The big question everyone is asking is: 'Will it increase the premiums?' If you are being dropped by your employer and you are going into the exchanges, it depends on how much much money you are making. In New York, for instance, the rate in the exchange is cheaper than the group markets."

The Kaiser Family Foundation published a report earlier this month which worked out the cost of premiums in 17 states plus DC.

To hourly workers, many of whom are living below the poverty line, a small increase in healthcare costs can represent the final straw for their already stretched family budgets.

The wife of a Trader Joe's part-time worker who contacted the Guardian in response to a callout said her husband was so concerned about potential cost increases, he was considering not buying healthcare insurance at all.

The mother of two, who did not want her name published, said: "My husband is debating getting insurance which scares me as the job is physical so there is always a risk of on site injuries that require medical attention. We are expecting to pay more out of pocket. We are working on putting aside some now so we can afford coverage next year.

"I am worried there will be months when we will have to choose paying health insurance or paying a bill. Neither is a good option with two children to think of."

People without health coverage in 2014 may have to pay a fine of up to $95 per person and 100% of their healthcare costs.

She told the Guardian that she and her children had been covered by her husband's company, Trader Joe's, until he was informed in August that, as a part-time worker of 30 hours or less, his healthcare benefits would no longer be paid when the ACA comes into effect. An internal memo by Trader Joe's announced that each affected employee would be given $500 and said it hoped that "many of you should be able to obtain healthcare coverage at very little if any net cost to you".

A college student, she said her research had shown that the cost of an alternative plan would be greater than the $500 they will receive. Her husband previously paid $99 for coverage, she said.

She said she felt let down. "Finding out that we were losing health benefits seems (coupled with the previous reduction in contributions to retirement) like the company has reached a size/level will it no longer makes sense to put employees first. This makes me very sad."

Unions and worker's organisation say that, at a time of growing concerns over the level of minimum wage earned by the nation's lowest paid workers, it is the same workers who are being worst hit by the changes, ahead of the ACA.

David Wehde, organising director of Working America, an affiliate of AFL-CIO with three and a half million members, said: "What we are hearing from our workers is a lot of frustration, particularly lower wage workers in retail or service jobs."

However, Wahde said there is "huge scepticism" of the claims made by some employers that they had been forced to make changes in benefits because of the costs of the ACA.

"Our workers are frustrated, saying that their employers don't have to do it this way, but they are just using the ACA as an excuse" said Wehde. "It is not winning workers' trust."

Janna Pea, the deputy communications director of the Retail Wholesale and Department Stores Union, said the shift some employers were taking towards part time workers was an unfortunate side effect of the ACA.

Pea said: "We are hearing from our members who are concerned about what is happening with their companies. Not only are they looking at having their healthcare coverage cut they are also looking at less hours."

"You have a trend where employers are saying they have no obligation to do anything for anybody who works less than 30 hours a week. Part of the act created incentives for employers to take away benefits from employees. It is an unfortunate side effect. The act ignores part time workers."

Karen McVeigh has been a senior news reporter for the Guardian since December 2006. Before that, she freelanced for the Times following a five-year stint as The Scotsman's London Correspondent.